<template>
  <div class="pagination">
    <!-- 左 -->
    <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo-1)">上一页</button>
    <button v-if="startNum_endNum.start > 1" @click="$emit('getPageNo', 1)">1</button>
    <button v-if="startNum_endNum.start > 2">···</button>
    <!-- 中 -->
    <template v-for="(page, index) in startNum_endNum.end">
      <button :class="{active: pageNo == page}" :key="index" v-if="page >= startNum_endNum.start" @click="$emit('getPageNo', page)">
        {{ page }}
      </button>
    </template>

    <!-- 右 -->
    <button v-if="startNum_endNum.end < totalPage - 1">···</button>
    <button v-if="startNum_endNum.end < totalPage" @click="$emit('getPageNo', totalPage)">{{ totalPage }}</button>
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo', pageNo+1)">下一页</button>

    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>
  
  <script>
export default {
  name: "Pagination",
  props: ["pageNo", "pageSize", "total", "continues"],
  computed: {
    // 总页数
    totalPage() {
      return Math.ceil(this.total / this.pageSize);
    },
    // 连续的页码的起始与结束的数字
    startNum_endNum() {
      const { pageNo, totalPage, continues } = this;
      // 初始化两个变量start、end, 用于记录连续页码的起始和结束位置
      let start = 0,
        end = 0;
      // 总页数小于连续的页数时
      if (continues > totalPage) {
        start = 1;
        end = totalPage;
      } else {
        // 总页数大于连续的页数时
        // 计算出起始和结束位置
        start = pageNo - parseInt(continues / 2);
        end = pageNo + parseInt(continues / 2);
        // 排除不正常情况(如起始位置页码值<1, 结束位置的值>总页数)
        if (start < 1) {
          start = 1;
          end = continues;
        }
        if (end > totalPage) {
          // end=32, totalPage=31, pageNo=30, continues=5
          end = totalPage; // end = 31     27 28 29 30 31
          start = totalPage - continues + 1; // start = 27
        }
      }
      return { start, end };
    },
  },
};
</script>
  
  <style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>